M530l2 c1

Cleaned or PEI-coated cover glasses were placed in a sealed PTFE-ring and each surface was covered with 1 ml of a 10% ethanol (AppliChem, Germany) HEPES-buffer mixture pH = 7.0. 100 μl of a suspension containing COOH-functionalized particles (section 2.2) was added dropwise afterwards. After a period of 15 min, sedimentation of the particles was completed and the probes and their corresponding radial profiles were imaged using an inverted microscope (Olympus IX73, Germany) with an integrated halogen lamp for bright-field microscopy. To obtain the respective interference reflection patterns, samples were illuminated by a monochromatic 530 nm collimated LED (M530L2-C1, Thorlabs, Germany). An Olympus 60x, NA (numerical aperture) 1.35 oil-immersion objective (UPlanSApo 60x 1.35 oil, Olympus, Germany) was used in concert with a quarter waveplate (WPMQ05M-532, Thorlabs GmbH, Germany), placed on the microscope’s breadboard between objective and sample, as well as additional polarizers to avoid internal reflections [19 (link)]. Images were captured with a monochrome CCD camera (DMK 23U274, ImagingSource, Germany) using μManager microscopy software. All datasets were recorded applying an exposure time of 50 ms and stored in tagged image file format (tiff). Besides the methods explained in the following sections, no image processing was performed.